Fuel cells provide electricity from chemical oxidation-reduction reactions and possess significant advantages over other forms of power generation in terms of cleanliness and efficiency. Typically, fuel cells employ hydrogen as the fuel and oxygen as the oxidizing agent. The power generation is proportional to the consumption rate of the reactants.
A significant disadvantage which inhibits the wider use of fuel cells is the lack of a widespread hydrogen infrastructure. Hydrogen has a relatively low volumetric energy density and is more difficult to store and transport than the hydrocarbon fuels currently used in most power generation systems. One way to overcome this difficulty is the use of reformers to convert the hydrocarbons to a hydrogen rich gas stream which can be used as a feed for fuel cells.
Hydrocarbon-based fuels, such as natural gas, LPG, gasoline, and diesel, require conversion processes to be used as fuel sources for most fuel cells. Current art uses multi-step processes combining an initial conversion process with several clean-up processes. The initial process is most often steam reforming (SR), autothermal reforming (ATR), catalytic partial oxidation (CPOX), or non-catalytic partial oxidation (POX). The clean-up processes are usually comprised of a combination of desulfurization, high temperature water-gas shift, low temperature water-gas shift, selective CO oxidation, or selective CO methanation. Alternative processes include hydrogen selective membrane reactors and filters.
Despite the above work, there remains a need for a simple unit for converting a hydrocarbon fuel to a hydrogen rich gas stream for use in conjunction with a fuel cell.
The present invention is generally directed to an apparatus and method for converting hydrocarbon fuel into a hydrogen rich gas. In one illustrative embodiment of the present invention, the apparatus for converting hydrocarbon fuel into hydrogen rich gas includes a plurality of modules arranged radially along a common axis. Such an arrangement permits a compact design and highly efficient heat transfer between differing reactor modules. Depending upon the reaction taking place within the module, each module may include an annular layer of thermally insulating material disposed between the shell and the respective processing core. In a similar manner, a module may include a porous support member, such as screen, mesh, perforated plate, or porous sintered plate. Such a porous support member may be included so as to support and contain the contents of the module, particularly granular catalyst materials.
As noted above and described herein, the apparatus of the present invention is used to carry out a series of reactions that converts hydrocarbon fuel to hydrogen rich gas. In one illustrative embodiment of such an apparatus, the first module preferably has a processing core that includes a partial oxidation catalyst or alternatively a steam reforming catalyst or alternatively an autothermal reforming catalyst or alternatively combinations and/or mixtures of such catalysts. A second module positioned adjacent to the first module is preferably designed so that the processing core of the second module includes a first heat exchanger. Such a heat exchanger may be a fin-typed heat exchanger, tubing heat exchanger, heat pipe, or similar means that are capable of exchanging heat.
Within the plurality of modules, a third module is preferably positioned adjacent to the second module, the processing core of the third module including a desulfurizing agent. A wide variety of desulfurizing agents may be used but preferably the desulfurizing agent includes zinc oxide. A fourth module positioned adjacent to and in fluid communication with the third module includes a processing core containing a water gas shift catalyst. One of skill in the art should understand and appreciate that the water gas shift catalyst may be a low temperature water gas shift catalyst that includes a catalyst material selected from copper, copper oxide, zinc, platinum, rhenium, palladium, rhodium, and gold and combinations and mixtures of these an similar materials. Alternatively, the water gas shift catalyst is a high temperature water gas shift catalyst that includes a catalyst material selected from ferric oxide, chromic oxide, copper, iron silicide, platinum, palladium and other platinum group members, and combinations and mixtures of these and similar materials.
The apparatus is further designed to include within the plurality of modules a fifth module positioned adjacent to and in fluid communication with the fourth module. The processing core of the fifth module includes a second heat exchanger. Such a heat exchanger may include a fin-typed heat exchanger, tubing heat exchanger, heat pipe, or similar means that are capable of exchanging heat.
The plurality of modules further includes a sixth module positioned adjacent to the fifth module with which it is in fluid communication. The processing core of the sixth module includes a carbon monoxide oxidation catalyst that preferably includes a material selected from platinum, palladium, iron, chromium, manganese, iron oxide, chromium oxide, manganese oxide, ruthenium, gold, cerium, lanthanum, and combinations and mixtures of these and similar compounds.
The present invention also includes a process for converting hydrocarbon fuel into a hydrogen rich gas. One such illustrative process utilizes the apparatus disclosed herein. Such a process generally includes providing a fuel processor having a plurality of modules arranged radially along a common axis, each forming an annular reaction chamber. By feeding the hydrocarbon fuel successively through each of the above described modules in an generally radial direction a hydrogen rich gas is produced in a manner that optimizes space considerations and heat transfer considerations.